Programable Active Fixator System for Systematic In Vivo Investigation of Bone Healing Processes

Abstract

This manuscript introduces a programable active bone fixator system that enables systematic investigation of bone healing processes in a sheep animal model. In contrast to previous systems, this solution combines the ability to precisely control the mechanical conditions acting within a fracture with continuous monitoring of the healing progression and autonomous operation of the system throughout the experiment. The active fixator system was implemented on a double osteotomy model that shields the experimental fracture from the influence of the animal’s functional loading. A force sensor was integrated into the fixator to continuously measure stiffness of the repair tissue as an indicator for healing progression. A dedicated control unit was developed that allows programing of different loading protocols which are later executed autonomously by the active fixator. To verify the feasibility of the system, it was implanted in two sheep with different loading protocols, mimicking immediate and delayed weight-bearing, respectively. The implanted devices operated according to the programmed protocols and delivered seamless data over the whole course of the experiment. The in vivo trial confirmed the feasibility of the system. Hence, it can be applied in further preclinical studies to better understand the influence of mechanical conditions on fracture healing.

Can Optimizing the Mechanical Environment Deliver a Clinically Significant Reduction in Fracture Healing Time?

“…Our group recently developed a system [ 41 ] for the continuous measurement of repair tissue stiffness. Using this model, we can assess the mechanical competence of fracture repair tissue without sacrificing multiple animals at different time points.…”

Short-Term Bone Healing Response to Mechanical Stimulation—A Case Series Conducted on Sheep

“…The motion of the active fixator was regulated by a custom-made control unit [19] that was directly attached to the fixator frame and which autonomously executed the programmed stimulation protocol. For each stimulation cycle, the displacement of the mobile bone fragment and the corresponding force was measured and the data was recorded in the internal memory of the control unit.…”

“…The study was approved by the local ethics committee (Canton of Grisons, Switzerland, approval: TVB 2017_23, 01/09/2017 and conducted under our AAALAC accredited roof. The surgeries were performed on the right The motion of the active fixator was regulated by a custom-made control unit [19] that was directly attached to the fixator frame and which autonomously executed the programmed stimulation protocol. For each stimulation cycle, the displacement of the mobile bone fragment and the corresponding force was measured and the data was recorded in the internal memory of the control unit.…”

“…To circumvent this problem, Tufekci et al [11] applied controlled interfragmentary motion in a sheep tibia model with an active motorized fixator on a double osteotomy, thus, eliminating the effect of functional loading. In our previous work [19], we further enhanced Tufekci's fixator by integrating an implanted force sensor to continuously measure the stiffness progression of the repair tissue and developed a control unit that permits the programming of arbitrary stimulation protocols, which are executed autonomously by the active fixator.…”

“…In this study, we employed the previously described model [11,19] to apply a wellcontrolled stimulation protocol composed of stimulation and resting periods in a sheep tibial fracture model, and continuously measured fracture stiffness to investigate the evolution of the mechanical competence of the fracture repair tissue. We aimed to observe the short-term response of the repair tissue with special reference to the role of resting periods in fracture healing.…”